Djilali Belaid / AFP - Getty Images

An image grab taken from AFP TV shows a Syrian boy holding a Kalashnikov as he is comforted by a rebel during fighting with government forces at the Crac des Chevaliers near the village of Azzara on the outskirts of the flashpoint city of Homs on June 28, 2012. Protected by the night, Syrian rebels climb on board motorcycles, lights off, on their way to the Crac des Chevaliers, a crusader castle which they are fiercely defending against government forces who continue to attack the area with tanks and artillery.

Agence France Presse (AFP) reports that Syrian rebel fighters are engaged in a fierce battle at the Crac des Chevaliers, a medieval castle dating back to the time of the Crusades. The Free Syrian Army is desperate to hold on to the fortress and even teenagers are joining the fighting, according to AFP.

Last month, the U.N.'s Special Representative for Children and Armed Conflict criticized the rebellion's main armed group for its treatment of children.

"For the first time we heard of children being recruited by the Free Syrian Army mainly in medical and service orientated jobs but still on the front line," Radhika Coomaraswamy told the BBC.

See more of Djilali Belaid's images of the fight for Azzara on PhotoBlog, and watch his video report about the battle for the castle.

Related content:

• Syria rebels come to blows while seeking peace
• 'Catastrophe': Journalist behind the lines in Syria sees no end to war
• Rights group: Syria's 20 ways to torture prove its crimes against humanity
• Glimpses of escalating conflict in Syria

Follow @msnbc_pictures